Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

Role and Evolution of Nanoparticle Structure and Chemical State during the Oxidation of NO over Size- and Shape-Controlled Pt/γ-Al2O3 Catalysts under Operando Conditions

Abstract: The structure and chemical state of size-selected Pt nanoparticles (NPs) supported on γ-Al2O3 were studied during the oxidation of NO using X-ray absorption near-edge spectroscopy and extended X-ray absorption fine-structure spectroscopy measurements under operando conditions. The data revealed the formation of PtOx species in the course of the reaction that remained present at the maximum temperature studied, 350 °C. The PtOx species were found in all samples, but those with the smallest NPs showed the highest degree of oxidation. Moreover, NO-induced nanoparticle redispersion was observed at temperatures below 150 °C for all catalysts studied. Catalytic tests showed activity toward the oxidation of NO for all samples. Nevertheless, the catalyst with the smallest NPs was found to be the least active, which is explained by a more extensive formation of PtOx species in this catalyst and their detrimental contribution to the oxidation of NO.

Physical structure and optical properties of Co-doped ZnO nanoparticles prepared by co-precipitation

Abstract: The structural and optical properties of cobalt-doped zinc oxide (Co-doped ZnO) nanoparticles have been investigated. The nanopowder with Co concentrations up to 5 at% was synthesized by a co-precipitation method. The physical structure and the chemical states of the Co-doped ZnO were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV–Visible reflectance and cathodoluminescence (CL) spectroscopy. The results show that cobalt ions predominantly occupy Zn2+ sites in the wurtzite crystal lattice and possess a valence state of 2+. CL analysis revealed that the incorporation of Co2+ creates a new emission band at 1.85 eV, but quenched the near-band-edge luminescence.

Effects of Iron Addition on Material Characteristics and Pseudo-Capacitive Behavior of Mn-Oxide Electrodes

Abstract: Iron addition was attempted in this study to improve the pseudo-capacitive property of Mn oxides. The oxides were prepared on graphite substrates by anodic deposition. The deposition solutions were 0.25 M manganese acetate MnCH3COO2 aqueous solutions with various amount of FeCl3 up to 0.15 M. Crystal structure and surface morphology of the deposited oxides were examined by X-ray diffraction and scanning electron microscopy, while their chemical state was analyzed by X-ray photoelectron spectroscopy and X-ray absorption near edge structure. Moreover, specific capacitances of the oxide electrodes were determined by cyclic voltammetry in 2 M KCl electrolyte. Experimental results indicated that the incorporated iron presented as divalent and trivalent forms in the binary oxides. Although iron addition did not change the nanocrystalline structure of the deposited Mn oxide, it caused the chemical state and surface morphology variations of the oxide electrodes. Consequently, their pseudo-capacitive performances were modified. The optimum specific capacitance of 212 F g1 was found for the oxide deposited in the solution containing 0.05 M FeCl3. The value was 21% higher than that of the plain Mn oxide. Capacitance-retained ratio of the oxide after 1000 charge-discharge cycles was also improved from 70 to 85% because of iron addition.

Low-temperature CO oxidation at persistent low-valent Cu nanoparticles on TiO2 aerogels

Abstract: We exploit interfacial charge transfer from titania (TiO2) to copper (Cu) to design catalytic Cu/TiO2 composite aerogels that shift the chemical state of Cu nanoparticles away from Cu2+, making them highly active for low-temperature CO oxidation. The high degree of interfacial contact between ∼2–3 nm–diameter Cu particles and the networked ∼10 nm–diameter TiO2 particles in ultraporous aerogel stabilizes a high ratio of Cu0/1+:Cu2+. The reduced nature of Cu in Cu/TiO2 aerogels is evidenced by a strong surface plasmon resonance in its diffuse reflectance UV–vis spectrum, by its X-ray photoelectron spectral features, and by infrared spectroscopic evidence of CO binding at the catalyst surface. In contrast, when larger diameter (∼50–60 nm), non–networked TiO2 particles are used to support Cu nanoparticles, the single planar nanoscale interface between Cu and the support particle stabilizes a much lower fraction of low-valent Cu. The Cu0/1+ speciation stabilized within the aerogel catalyzes low-temperature CO oxidation (